Frataxin Mutants

ABSTRACT

Described herein are compositions and methods for treating Friedreich&#39;s Ataxia (FRDA). In some aspects, mutant forms of frataxin which are resistant to ubiquitination are provided. In some aspects, pharmaceutical compositions comprising mutant frataxin are provided. In further aspects, methods of using mutant frataxin are provided.

RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S. App. No.61/368,576 filed on Jul. 28, 2010, which is hereby incorporated byreference in its entirety for all purposes.

FIELD

The present invention relates generally to compositions and methodsuseful for the treatment of Friedreich's Ataxia (FRDA). Morespecifically, the invention relates to the identification of a mutantfrataxin protein and methods of delivering said protein into cells.

BACKGROUND

The disease. FRDA is an orphan disease that affects >20,000 individualsin Caucasian populations. Generally within 10 to 15 years from onset itleads to loss of deambulation and complete disability, with prematuredeath often caused by cardiac insufficiency. Symptoms usually appearlate in the first decade or early in the second decade of life, andinclude gait instability and general clumsiness. Gait ataxia has bothcerebellar and sensory features, involves truncus and limbs, and is bothprogressive and generally unremitting. Swaying is common and, as itbecomes more severe, eventually requires constant support and wheelchairuse. Dysarthria occurs early in the disease and ultimately leads tocomplete speech impairment. Furthermore, dysphagia is a late feature andmay require artificial feeding. Loss of peripheral neurons in dorsalroot ganglia is the preeminent pathological finding. Ventricularhypertrophy characterizes the cardiac picture, and may progressivelylead to congestive heart failure and fatal arrhythmias. A significantminority of patients also develop diabetes mellitus via mechanisms thatare not yet clearly defined.

FRDA is caused by homozygous hyperexpansion of GAA triplets within thefirst intron of FXN, a highly conserved five-exon gene located on thelong arm of human chromosome 9, coding for the protein frataxin.Pathological GAA expansions (from ˜70 to >1,000 triplets) result in“sticky” DNA structures and epigenetic changes that severely reducetranscription of the FXN gene. FRDA patients live with 10-30% residualfrataxin, and the severity of the disease is usually proportional to thenumber of GAA triplets and the consequent degree of frataxin reduction.A minority of FRDA patients, so-called compound heterozygotes, haspathological GAA expansions on one FXN allele and loss-of-functionmutations on the other.

Current therapeutic approaches. There is currently no specific therapyto prevent the progression of the disease. Most therapeutic approachesare aimed at reducing mitochondrial dysfunction and iron overload, andare therefore based on the use of anti-oxidants or iron chelators.Idebenone, a synthetic analog of ubiquinone with anti-oxidantproperties, is currently under evaluation in phase III clinical trials.The iron chelator deferiprone and Gingko-biloba extract are otheranti-oxidants presently in phase II clinical trials. Besides this, aslevels of residual frataxin are crucial in determining the severity ofthe disease, many efforts have been put into the identification ofmolecules that increase frataxin transcription. A new class of histonede-acetylase (HDAC) inhibitors has been shown to reverse FXN silencingin FRDA cells and is now undergoing pre-clinical evaluation. Theperoxisome proliferator-activated receptor gamma (PPAR-gamma) agonistAzelaoyl PAF has also recently been shown to increase FXN transcription,and a series of PPAR-gamma agonists are currently in pre-clinical phase.Another PPAR-gamma agonist, the widely used anti-diabetic pioglitazone,is entering a phase III trial for FRDA treatment. Finally, it was shownthat erithropoietin appears to increase frataxin levels by an unknownmechanism. Recombinant erithropoietin as a treatment for FRDA iscurrently in phase II clinical trials.

While numerous approaches to treating FRDA have been explored, each ofthose approaches has significant limitations. Thus, a need exists in theart for new methods for more effectively treating FRDA.

SUMMARY

The present disclosure addresses long-felt needs in the field ofmedicine by providing novel compositions and methods for treatingFriedreich's Ataxia.

Briefly stated, the present disclosure provides methods and compositionsfor the treatment of Friedreich's Ataxia (FRDA). The present disclosurerelates to novel frataxin mutants, nucleotides encoding those frataxinmutants, methods of delivering the frataxin mutants, and methods oftreating FRDA using the frataxin mutants.

In some aspects, the present disclosure provides isolated polypeptidehaving at least 75%, 80%, 85%, 90%, 95%, 98%, or 99% sequence identityto the amino acid sequence of FIG. 1 and comprising an R residue at aposition corresponding to position 147 of FIG. 1.

In some aspects, the present disclosure provides for isolated nucleicacid molecule comprising a nucleic acid sequence which encodes apolypeptide having at least 75%, 80%, 85%, 90%, 95%, 98%, or 99%sequence identity to the amino acid sequence of FIG. 1.

In some aspects, the present disclosure provides for isolated nucleicacid molecules, wherein the nucleic acid molecule comprises a nucleotidesequence having at least 75%, 80%, 85%, 90%, 95%, 98%, or 99% sequenceidentity to the full length sequence of FIG. 2.

In some aspects, the present disclosure provides for pharmaceuticalcompositions comprising a therapeutically effective amount of theisolated polypeptide of the present disclosure, optionally together withone or more pharmaceutically acceptable excipients, diluents,preservatives, solubilizers, emulsifiers, adjuvants, or carriers.

In further aspects, the present disclosure provides for methods oftreating Friedreich's Ataxia, comprising administering to a subject thepharmaceutical compositions of the present disclosure.

In certain aspects, the present disclosure provides for methods ofdelivering the isolated polypeptide of any the present disclosure into acell by a carrier selected from the group consisting of a liposome, apolymeric microcarrier, an exosome, a bacterial carrier, and afunctional equivalent thereof. In further aspects, the isolatedpolypeptide has been fused in frame with a protein transduction domain.In still further aspects, the isolated polypeptide is delivered into thecell of a subject having Friedreich's Ataxia.

In some aspects, the present disclosure provides for methods ofdelivering the isolated polypeptide of the present disclosure into acell by a carrier system selected from the group consisting of a viralsystem, a hybrid synthetic-viral system, a non-viral system, and afunctional equivalent thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the amino acid sequence of frataxin (SEQ ID NO:1). Aminoacids 1-210 represent the frataxin precursor, and the italicizedsequence (81-210) corresponds to the mature frataxin. The lysine atposition 147 has been underlined.

FIG. 2 shows the nucleotide sequence of the FXN gene, which encodes thehuman protein frataxin.

FIG. 3A shows 293 Flp-In cells stably expressing frataxin¹⁻²¹⁰(293-frataxin) or the K147R frataxin mutant (293-frataxin K147R). Cellswere treated for the indicated times with 100 μg/ml cycloheximide (CHX)to block new protein synthesis. Proteins were resolved on SDS-PAGE andrevealed with anti-frataxin antibody or anti-tubulin as a loadingcontrol. Pre: frataxin precursor. One representative experiment out ofthree performed with similar results is shown.

FIG. 3B shows densitometric analysis of frataxin precursor levels asshown in FIG. 3A normalized to tubulin levels. The graph shows thetime-dependent decline upon CHX treatment. WT: 293-frataxin cells,K147R: 293-frataxin K147R cells.

FIG. 4 shows HeLa cells that were transiently transfected with HA-taggedfrataxin¹⁻²¹⁰ or the HA-tagged K147R frataxin mutant. Protein extractsat the indicated days after transfection were resolved on SDS-PAGE andrevealed with anti-HA antibody or anti-tubulin as a loading control.Pre: frataxin precursor; int: intermediate; mat: mature; tub: tubulin.One representative experiment out of three performed with similarresults is shown.

DETAILED DESCRIPTION

The following explanations of terms and methods are provided to betterdescribe the present disclosure and to guide those of ordinary skill inthe art in the practice of the present disclosure. As used herein,“comprising” means “including” and the singular forms “a” or “an” or“the” include plural references unless the context clearly dictatesotherwise. For example, reference to “comprising a cell” includes one ora plurality of such cells, and so forth. The term “or” refers to asingle element of stated alternative elements or a combination of two ormore elements, unless the context clearly indicates otherwise.

Unless explained otherwise, all technical and scientific terms usedherein have the same meaning as commonly understood to one of ordinaryskill in the art to which this disclosure belongs. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present disclosure, suitable methods andmaterials are described below. The materials, methods, and examples areillustrative only and not intended to be limiting. Other features of thedisclosure are apparent from the following detailed description and theclaims.

Certain terms are discussed herein to provide additional guidance to thepractitioner in describing the compositions, devices, methods and thelike of aspects of the invention, and how to make or use them. It willbe appreciated that the same thing can be said in more than one way.Consequently, alternative language and synonyms can be used for any oneor more of the terms discussed herein. No significance is to be placedupon whether or not a term is elaborated or discussed herein. Somesynonyms or substitutable methods, materials and the like are provided.Recital of one or a few synonyms or equivalents does not exclude use ofother synonyms or equivalents, unless it is explicitly stated. Use ofexamples, including examples of terms, is for illustrative purposes onlyand does not limit the scope and meaning of the aspects of the inventionherein.

All publications disclosed herein are incorporated by reference in theirentirety for all purposes.

The term “peptide” as used herein refers to a short polypeptide, e.g.,one that is typically less than about 50 amino acids long and moretypically less than about 30 amino acids long. The term as used hereinencompasses analogs and mimetics that mimic structural and thusbiological function.

The term “isolated protein” or “isolated polypeptide” is a protein orpolypeptide that by virtue of its origin or source of derivation (1) isnot associated with naturally associated components that accompany it inits native state, (2) exists in a purity not found in nature, wherepurity can be adjudged with respect to the presence of other cellularmaterial (e.g., is free of other proteins from the same species) (3) isexpressed by a cell from a different species, or (4) does not occur innature (e.g., it is a fragment of a polypeptide found in nature or itincludes amino acid analogs or derivatives not found in nature orlinkages other than standard peptide bonds). Thus, a polypeptide that ischemically synthesized or synthesized in a cellular system differentfrom the cell from which it naturally originates will be “isolated” fromits naturally associated components. A polypeptide or protein may alsobe rendered substantially free of naturally associated components byisolation, using protein purification techniques well known in the art.As thus defined, “isolated” does not necessarily require that theprotein, polypeptide, peptide or oligopeptide so described has beenphysically removed from its native environment.

The term “polypeptide fragment” as used herein refers to a polypeptidethat has a deletion, e.g., an amino-terminal and/or carboxy-terminaldeletion compared to a full-length polypeptide. In a preferredembodiment, the polypeptide fragment is a contiguous sequence in whichthe amino acid sequence of the fragment is identical to thecorresponding positions in the naturally-occurring sequence. Fragmentstypically are at least 5, 6, 7, 8, 9 or 10 amino acids long, preferablyat least 12, 14, 16 or 18 amino acids long, more preferably at least 20amino acids long, more preferably at least 25, 30, 35, 40 or 45, aminoacids, even more preferably at least 50 or 60 amino acids long, and evenmore preferably at least 70 amino acids long.

A protein has “homology” or is “homologous” to a second protein if thenucleic acid sequence that encodes the protein has a similar sequence tothe nucleic acid sequence that encodes the second protein.Alternatively, a protein has homology to a second protein if the twoproteins have “similar” amino acid sequences. (Thus, the term“homologous proteins” is defined to mean that the two proteins havesimilar amino acid sequences.) As used herein, homology between tworegions of amino acid sequence (especially with respect to predictedstructural similarities) is interpreted as implying similarity infunction.

When “homologous” is used in reference to proteins or peptides, it isrecognized that residue positions that are not identical often differ byconservative amino acid substitutions. A “conservative amino acidsubstitution” is one in which an amino acid residue is substituted byanother amino acid residue having a side chain (R group) with similarchemical properties (e.g., charge or hydrophobicity). In general, aconservative amino acid substitution will not substantially change thefunctional properties of a protein. In cases where two or more aminoacid sequences differ from each other by conservative substitutions, thepercent sequence identity or degree of homology may be adjusted upwardsto correct for the conservative nature of the substitution. Means formaking this adjustment are well known to those of skill in the art. See,e.g., Pearson, 1994, Methods Mol. Biol. 24:307-31 and 25:365-89 (hereinincorporated by reference).

The following six groups each contain amino acids that are conservativesubstitutions for one another: 1) Serine (S), Threonine (T); 2) AsparticAcid (D), Glutamic Acid (E); 3) Asparagine (N), Glutamine (Q); 4)Arginine (R), Lysine (K); 5) Isoleucine (I), Leucine (L), Methionine(M), Alanine (A), Valine (V), and 6) Phenylalanine (F), Tyrosine (Y),Tryptophan (W). Table 1 is a general BLOSUM62 amino acid substitutionmatrix.

TABLE 1 BLOSUM62 amino acid substitution matrix. A B C D E F G H I K L MN P Q R S T V W X Y Z A 4 −2 0 −2 −1 −2 0 −2 −1 −1 −1 −1 −2 −1 −1 −1 1 00 −3 −1 −2 −1 B −2 6 −3 6 2 −3 −1 −1 −3 −1 −4 −3 1 −1 0 −2 0 −1 −3 −4 −1−3 2 C 0 −3 9 −3 −4 −2 −3 −3 −1 −3 −1 −1 −3 −3 −3 −3 −1 −1 −1 −2 −1 −2−4 D −2 6 −3 6 2 −3 −1 −1 −3 −1 −4 −3 1 −1 0 −2 0 −1 −3 −4 −1 −3 2 E −12 −4 2 5 −3 −2 0 −3 1 −3 −2 0 −1 2 0 0 −1 −2 −3 −1 −2 5 F −2 −3 −2 −3 −36 −3 −1 0 −3 0 0 −3 −4 −3 −3 −2 −2 −1 1 −1 3 −3 G 0 −1 −3 −1 −2 −3 6 −2−4 −2 −4 −3 0 −2 −2 −2 0 −2 −3 −2 −1 −3 −2 H −2 −1 −3 −1 0 −1 −2 8 −3 −1−3 −2 1 −2 0 0 −1 −2 −3 −2 −1 2 0 I −1 −3 −1 −3 −3 0 −4 −3 4 −3 2 1 −3−3 −3 −3 −2 −1 3 −3 −1 −1 −3 K −1 −1 −3 −1 1 −3 −2 −1 −3 5 −2 −1 0 −1 12 0 −1 −2 −3 −1 −2 1 L −1 −4 −1 −4 −3 0 −4 −3 2 −2 4 2 −3 −3 −2 −2 −2 −11 −2 −1 −1 −3 M −1 −3 −1 −3 −2 0 −3 −2 1 −1 2 5 −2 −2 0 −1 −1 −1 1 −1 −1−1 −2 N −2 1 −3 1 0 −3 0 1 −3 0 −3 −2 6 −2 0 0 1 0 −3 −4 −1 −2 0 P −1 −1−3 −1 −1 −4 −2 −2 −3 −1 −3 −2 −2 7 −1 −2 −1 −1 −2 −4 −1 −3 −1 Q −1 0 −30 2 −3 −2 0 −3 1 −2 0 0 −1 5 1 0 −1 −2 −2 −1 −1 2 R −1 −2 −3 −2 0 −3 −20 −3 2 −2 −1 0 −2 1 5 −1 −1 −3 −3 −1 −2 0 S 1 0 −1 0 0 −2 0 −1 −2 0 −2−1 1 −1 0 −1 4 1 −2 −3 −1 −2 0 T 0 −1 −1 −1 −1 −2 −2 −2 −1 −1 −1 −1 0 −1−1 −1 1 5 0 −2 −1 −2 −1 V 0 −3 −1 −3 −2 −1 −3 −3 3 −2 1 1 −3 −2 −2 −3 −20 4 −3 −1 −1 −2 W −3 −4 −2 −4 −3 1 −2 −2 −3 −3 −2 −1 −4 −4 −2 −3 −3 −2−3 11 −1 2 −3 X −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1 −1−1 −1 −1 −1 Y −2 −3 −2 −3 −2 3 −3 2 −1 −2 −1 −1 −2 −3 −1 −2 −2 −2 −1 2−1 7 −2 Z −1 2 −4 2 5 −3 −2 0 −3 1 −3 −2 0 −1 2 0 0 −1 −2 −3 −1 −2 5Reference: Henikoff, S. and Henikoff, J. G. (1992). Amino acidsubstitution matrices from protein blocks. Proc. Natl. Acad. Sci. USA89: 10915-10919.

Sequence homology for polypeptides, which is also referred to as percentsequence identity, is typically measured using sequence analysissoftware. See, e.g., the Sequence Analysis Software Package of theGenetics Computer Group (GCG), University of Wisconsin BiotechnologyCenter, 910 University Avenue, Madison, Wis. 53705. Protein analysissoftware matches similar sequences using a measure of homology assignedto various substitutions, deletions and other modifications, includingconservative amino acid substitutions. For instance, GCG containsprograms such as “Gap” and “Bestfit” which can be used with defaultparameters to determine sequence homology or sequence identity betweenclosely related polypeptides, such as homologous polypeptides fromdifferent species of organisms or between a wild-type protein and amutein thereof See, e.g., GCG Version 6.1.

A preferred algorithm when comparing a particular polypeptide sequenceto a database containing a large number of sequences from differentorganisms is the computer program BLAST (Altschul et al., J. Mol. Biol.215:403-410 (1990); Gish and States, Nature Genet. 3:266-272 (1993);Madden et al., Meth. Enzymol. 266:131-141 (1996); Altschul et al.,Nucleic Acids Res. 25:3389-3402 (1997); Zhang and Madden, Genome Res.7:649-656 (1997)), especially blastp or tblastn (Altschul et al.,Nucleic Acids Res. 25:3389-3402 (1997)).

Preferred parameters for BLASTp are: Expectation value: 10 (default);Filter: seg (default); Cost to open a gap: 11 (default); Cost to extenda gap: 1 (default); Max. alignments: 100 (default); Word size: 11(default); No. of descriptions: 100 (default); Penalty Matrix: BLOSUM62.

One skilled in the art may also use the ALIGN program incorporating thenon-linear algorithm of Myers and Miller (Comput. Appl. Biosci. (1988)4:11-17). For amino acid sequence comparison using the ALIGN program oneskilled in the art may use a PAM120 weight residue table, a gap lengthpenalty of 12, and a gap penalty of 4.

The length of polypeptide sequences compared for homology will generallybe at least about 16 amino acid residues, usually at least about 20residues, more usually at least about 24 residues, typically at leastabout 28 residues, and preferably more than about 35 residues. Whensearching a database containing sequences from a large number ofdifferent organisms, it is preferable to compare amino acid sequences.Database searching using amino acid sequences can be measured byalgorithms other than blastp known in the art. For instance, polypeptidesequences can be compared using FASTA, a program in GCG Version 6.1.FASTA provides alignments and percent sequence identity of the regionsof the best overlap between the query and search sequences. Pearson,Methods Enzymol. 183:63-98 (1990) (herein incorporated by reference).For example, percent sequence identity between amino acid sequences canbe determined using FASTA with its default parameters (a word size of 2and the PAM250 scoring matrix), as provided in GCG Version 6.1, hereinincorporated by reference.

Nucleic Acid Molecule: The term “nucleic acid molecule” or“polynucleotide” refers to a polymeric form of nucleotides of at least10 bases in length. The term includes DNA molecules (e.g., cDNA orgenomic or synthetic DNA) and RNA molecules (e.g., mRNA or syntheticRNA), as well as analogs of DNA or RNA containing non-natural nucleotideanalogs, non-native inter-nucleoside bonds, or both. The nucleic acidcan be in any topological conformation. For instance, the nucleic acidcan be single-stranded, double-stranded, triple-stranded, quadruplexed,partially double-stranded, branched, hair-pinned, circular, or in apadlocked conformation. If single stranded, the nucleic acid moleculecan be the sense strand or the antisense strand. “Nucleic acid molecule”includes nucleic acid molecules which are not naturally occurring.

Isolated: An “isolated” nucleic acid or polynucleotide (e.g., an RNA,DNA or a mixed polymer) is one which is substantially separated fromother cellular components that naturally accompany the nativepolynucleotide in its natural host cell, e.g., ribosomes, polymerases,and genomic sequences with which it is naturally associated. The termembraces a nucleic acid or polynucleotide that (1) has been removed fromits naturally occurring environment, (2) is not associated with all or aportion of a polynucleotide in which the “isolated polynucleotide” isfound in nature, (3) is operatively linked to a polynucleotide which itis not linked to in nature, or (4) does not occur in nature. The term“isolated” or “substantially pure” also can be used in reference torecombinant or cloned DNA isolates, chemically synthesizedpolynucleotide analogs, or polynucleotide analogs that are biologicallysynthesized by heterologous systems. However, “isolated” does notnecessarily require that the nucleic acid or polynucleotide so describedhas itself been physically removed from its native environment. Forinstance, an endogenous nucleic acid sequence in the genome of anorganism is deemed “isolated” herein if a heterologous sequence (i.e., asequence that is not naturally adjacent to this endogenous nucleic acidsequence) is placed adjacent to the endogenous nucleic acid sequence,such that the expression of this endogenous nucleic acid sequence isaltered. By way of example, a non native promoter sequence can besubstituted (e.g. by homologous recombination) for the native promoterof a gene in the genome of a human cell, such that this gene has analtered expression pattern. This gene would now become “isolated”because it is separated from at least some of the sequences thatnaturally flank it. A nucleic acid is also considered “isolated” if itcontains any modifications that do not naturally occur to thecorresponding nucleic acid in a genome. For instance, an endogenouscoding sequence is considered “isolated” if it contains an insertion,deletion or a point mutation introduced artificially, e.g. by humanintervention. An “isolated nucleic acid” also includes a nucleic acidintegrated into a host cell chromosome at a heterologous site, as wellas a nucleic acid construct present as an episome. Moreover, an“isolated nucleic acid” can be substantially free of other cellularmaterial, or substantially free of culture medium when produced byrecombinant techniques, or substantially free of chemical precursors orother chemicals when chemically synthesized. The term also embracesnucleic acid molecules and proteins prepared by recombinant expressionin a host cell as well as chemically synthesized nucleic acid moleculesand proteins.

The term “percent sequence identity” or “identical” in the context ofnucleic acid sequences refers to the nucleotides in the two sequenceswhich are the same when aligned for maximum correspondence. The lengthof sequence identity comparison may be over a stretch of at least aboutnine nucleotides, usually at least about 20 nucleotides, more usually atleast about 24 nucleotides, typically at least about 28 nucleotides,more typically at least about 32 nucleotides, and preferably at leastabout 36 or more nucleotides. There are a number of different algorithmsknown in the art which can be used to measure nucleotide sequenceidentity. For instance, polynucleotide sequences can be compared usingFASTA, Gap or Bestfit, which are programs in Wisconsin Package Version10.0, Genetics Computer Group (GCG), Madison, Wis. FASTA providesalignments and percent sequence identity of the regions of the bestoverlap between the query and search sequences. Pearson, MethodsEnzymol. 183:63-98 (1990) (hereby incorporated by reference in itsentirety). For instance, percent sequence identity between nucleic acidsequences can be determined using FASTA with its default parameters (aword size of 6 and the NOPAM factor for the scoring matrix) or using Gapwith its default parameters as provided in GCG Version 6.1, hereinincorporated by reference. Alternatively, sequences can be comparedusing the computer program, BLAST (Altschul et al., J. Mol. Biol.215:403-410 (1990); Gish and States, Nature Genet. 3:266-272 (1993);Madden et al., Meth. Enzymol. 266:131-141 (1996); Altschul et al.,Nucleic Acids Res. 25:3389-3402 (1997); Zhang and Madden, Genome Res.7:649-656 (1997)), especially blastp or tblastn (Altschul et al.,Nucleic Acids Res. 25:3389-3402 (1997)).

A particular, non-limiting example of a mathematical algorithm utilizedfor the comparison of sequences is that of Karlin and Altschul (Proc.Natl. Acad. Sci. (1990) USA 87:2264-68; Proc. Natl. Acad. Sci. USA(1993) 90: 5873-77) as used in the NBLAST and XBLAST programs (version2.0) of Altschul et al. (J. Mol. Biol. (1990) 215:403-10). BLASTnucleotide searches can be performed with the NBLAST program, score=100,wordlength=12 to obtain nucleotide sequences homologous to nucleic acidmolecules of the invention. To obtain gapped alignments for comparisonpurposes, Gapped BLAST can be utilized as described in Altschul et al.(Nucleic Acids Research (1997) 25(17):3389-3402). When utilizing BLASTand Gapped BLAST programs, the default parameters of the respectiveprograms (e.g., XBLAST and NBLAST) can be used (see website for BLASThosted by the National Center for Biotechnology Information).

Purified: The term purified does not require absolute purity; rather, itis intended as a relative term. Thus, for example, a purified productpreparation, is one in which the product is more concentrated than theproduct is in its environment within a cell. For example, a purified waxis one that is substantially separated from cellular components (nucleicacids, lipids, carbohydrates, and other peptides) that can accompany it.In another example, a purified wax preparation is one in which the waxis substantially free from contaminants, such as those that might bepresent following fermentation.

Recombinant: A recombinant nucleic acid molecule or protein is one thathas a sequence that is not naturally occurring, has a sequence that ismade by an artificial combination of two otherwise separated segments ofsequence, or both. This artificial combination can be achieved, forexample, by chemical synthesis or by the artificial manipulation ofisolated segments of nucleic acid molecules or proteins, such as geneticengineering techniques. Recombinant is also used to describe nucleicacid molecules that have been artificially manipulated, but contain thesame regulatory sequences and coding regions that are found in theorganism from which the nucleic acid was isolated.

“Specific binding” refers to the ability of two molecules to bind toeach other in preference to binding to other molecules in theenvironment. Typically, “specific binding” discriminates overadventitious binding in a reaction by at least two-fold, more typicallyby at least 10-fold, often at least 100-fold. Typically, the affinity oravidity of a specific binding reaction, as quantified by a dissociationconstant, is about 10⁻⁷ M or stronger (e.g., about 10⁻⁸ M, 10⁻⁹ M oreven stronger).

In general, “stringent hybridization” is performed at about 25° C. belowthe thermal melting point (T_(m)) for the specific DNA hybrid under aparticular set of conditions. “Stringent washing” is performed attemperatures about 5° C. lower than the T_(m) for the specific DNAhybrid under a particular set of conditions. The T_(m) is thetemperature at which 50% of the target sequence hybridizes to aperfectly matched probe. See Sambrook et al., Molecular Cloning: ALaboratory Manual, 2d ed., Cold Spring Harbor Laboratory Press, ColdSpring Harbor, N.Y. (1989), page 9.51, hereby incorporated by reference.For purposes herein, “stringent conditions” are defined for solutionphase hybridization as aqueous hybridization (i.e., free of formamide)in 6×SSC (where 20×SSC contains 3.0 M NaCl and 0.3 M sodium citrate), 1%SDS at 65° C. for 8-12 hours, followed by two washes in 0.2×SSC, 0.1%SDS at 65° C. for 20 minutes. It will be appreciated by the skilledworker that hybridization at 65° C. will occur at different ratesdepending on a number of factors including the length and percentidentity of the sequences which are hybridizing.

A preferred, non-limiting example of stringent hybridization conditionsincludes hybridization in 4×sodium chloride/sodium citrate (SSC), atabout 65-70° C. (or hybridization in 4×SSC plus 50% formamide at about42-50° C.) followed by one or more washes in 1×SSC, at about 65-70° C. Apreferred, non-limiting example of highly stringent hybridizationconditions includes hybridization in 1×SSC, at about 65-70° C. (orhybridization in 1×SSC plus 50% formamide at about 42-50° C.) followedby one or more washes in 0.3×SSC, at about 65-70° C. A preferred,non-limiting example of reduced stringency hybridization conditionsincludes hybridization in 4×SSC, at about 50-60° C. (or alternativelyhybridization in 6×SSC plus 50% formamide at about 40-45° C.) followedby one or more washes in 2×SSC, at about 50-60° C. Intermediate rangese.g., at 65-70° C. or at 42-50° C. are also within the scope of theinvention. SSPE (1×SSPE is 0.15 M NaCl, 10 mM NaH₂PO₄, and 1.25 mM EDTA,pH 7.4) can be substituted for SSC (1×SSC is 0.15 M NaCl and 15 mMsodium citrate) in the hybridization and wash buffers; washes areperformed for 15 minutes each after hybridization is complete. Thehybridization temperature for hybrids anticipated to be less than 50base pairs in length should be 5-10° C. less than the meltingtemperature (T_(m)) of the hybrid, where T_(m) is determined accordingto the following equations. For hybrids less than 18 base pairs inlength, T_(m) (° C.)=2(# of A+T bases)+4(# of G+C bases). For hybridsbetween 18 and 49 base pairs in length, T_(m)(°C.)=81.5+16.6(log₁₀[Na⁺])+0.41 (% G+C)−(600/N), where N is the number ofbases in the hybrid, and [Na⁺] is the concentration of sodium ions inthe hybridization buffer ([Na⁺] for 1×SSC=0.165 M).

The skilled practitioner recognizes that reagents can be added tohybridization and/or wash buffers. For example, to decrease non-specifichybridization of nucleic acid molecules to, for example, nitrocelluloseor nylon membranes, blocking agents, including but not limited to, BSAor salmon or herring sperm carrier DNA and/or detergents, including butnot limited to, SDS, chelating agents EDTA, Ficoll, PVP and the like canbe used. When using nylon membranes, in particular, an additional,non-limiting example of stringent hybridization conditions ishybridization in 0.25-0.5M NaH₂PO₄, 7% SDS at about 65° C., followed byone or more washes at 0.02M NaH₂PO₄, 1% SDS at 65° C. (Church andGilbert (1984) Proc. Natl. Acad. Sci. USA 81:1991-1995,) or,alternatively, 0.2×SSC, 1% SDS.

The term “substantial homology” or “substantial similarity,” whenreferring to a nucleic acid or fragment thereof, indicates that, whenoptimally aligned with appropriate nucleotide insertions or deletionswith another nucleic acid (or its complementary strand), there isnucleotide sequence identity in at least about 71%, 72%, 73%, 74%, 75%,76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, preferably at leastabout 90%, and more preferably at least about 95%, 96%, 97%, 98% or 99%of the nucleotide bases, as measured by any well-known algorithm ofsequence identity, such as FASTA, BLAST or Gap, as discussed above.

Alternatively, substantial homology or similarity exists when a nucleicacid or fragment thereof hybridizes to another nucleic acid, to a strandof another nucleic acid, or to the complementary strand thereof, understringent hybridization conditions. “Stringent hybridization conditions”and “stringent wash conditions” in the context of nucleic acidhybridization experiments depend upon a number of different physicalparameters. Nucleic acid hybridization will be affected by suchconditions as salt concentration, temperature, solvents, the basecomposition of the hybridizing species, length of the complementaryregions, and the number of nucleotide base mismatches between thehybridizing nucleic acids, as will be readily appreciated by thoseskilled in the art. One having ordinary skill in the art knows how tovary these parameters to achieve a particular stringency ofhybridization.

As used herein, a composition that is a “substantially pure” compound issubstantially free of one or more other compounds, i.e., the compositioncontains greater than 80 vol. %, greater than 90 vol. %, greater than 95vol. %, greater than 96 vol. %, greater than 97 vol. %, greater than 98vol. %, greater than 99 vol. %, greater than 99.5 vol. %, greater than99.6 vol. %, greater than 99.7 vol. %, greater than 99.8 vol. %, orgreater than 99.9 vol. % of the compound; or less than 20 vol. %, lessthan 10 vol. %, less than 5 vol. %, less than 3 vol. %, less than 1 vol.%, less than 0.5 vol. %, less than 0.1 vol. %, or less than 0.01 vol. %of the one or more other compounds, based on the total volume of thecomposition.

Vector: The term “vector” as used herein refers to a nucleic acidmolecule capable of transporting another nucleic acid to which it hasbeen linked. One type of vector is a “plasmid,” which refers to acircular double stranded DNA loop into which additional DNA segments maybe ligated. Other vectors include cosmids, bacterial artificialchromosomes (BACs) and yeast artificial chromosomes (YACs). Another typeof vector is a viral vector, wherein additional DNA segments may beligated into the viral genome (discussed in more detail below). Certainvectors are capable of autonomous replication in a host cell into whichthey are introduced (e.g., vectors having an origin of replication whichfunctions in the host cell). Other vectors can be integrated into thegenome of a host cell upon introduction into the host cell, and arethereby replicated along with the host genome. Moreover, certainpreferred vectors are capable of directing the expression of genes towhich they are operatively linked. Such vectors are referred to hereinas “recombinant expression vectors” (or simply, “expression vectors”). Avector can also include one or more selectable marker genes and othergenetic elements known in the art. Suitable vectors for use incyanobacteria include self-replicating plasmids (e.g., multiple copy andhigh-level expression) and chromosomal integration plasmids. Integrationof vectors into the host genome or autonomously replicating vectorsallow for gene expression in the host cell. When stable expressionresults from integration, the site of the construct's integration canoccur randomly within the host genome or can be targeted through the useof constructs containing regions of homology with the host genomesufficient to target recombination with the host locus. Where constructsare targeted to an endogenous locus, all or some of the transcriptionaland translational regulatory regions can be provided by the endogenouslocus.

Frataxin Mutants

Because the severity of FRDA corresponds inversely to frataxin levels inthe cell, most researchers have focused on the characterization ofmolecules that increase FXN transcription. Here, the present disclosureprovides a novel method of maintaining adequate cellular frataxinlevels, not by upregulating FXN transcription, but instead by developinga stable frataxin mutant precursor.

Human frataxin is synthesized as a 210 amino acid precursor (SEQ IDNO: 1) that is rapidly targeted to the mitochondria. Upon entrance intothe mitochondria, the frataxin precursor undergoes proteolyticprocessing that generates mature frataxin, a 130 amino acid globularpolypeptide that mostly resides within the mitochondrial matrix.Frataxin is involved in the proper functioning of the iron-sulfurcluster (ISC) machinery. Frataxin-defective cells in fact have reducedactivity of ISC-containing enzymes, a general imbalance in intracellulariron distribution and increased sensitivity to oxidative stress.Frataxin is extremely conserved across species, from bacteria to humans,and is not redundant yet is absolutely required for life in highereukaryotes.

It was observed that the frataxin precursor can be directly modified byubiquitin and consequently targeted to the proteasome for degradation.Ubiquitin binds most commonly to lysine residues on substrates, and inthe case of frataxin, it was determined that ubiquitination occurs attarget residue K147 (FIG. 1). By site-specific mutagenesis of K147, afrataxin mutant that is less easily ubiquitinated is generated. In oneembodiment, frataxin mutants have other than lysine at residue 147(relative to SEQ ID NO:1).

In one embodiment, frataxin mutants have arginine at residue 147.Alternatively, frataxin mutants have histidine at residue 147. Inanother alternative, residue 147 is serine, threonine, asparagine orglutamine. In another alternative residue 147 is glycine, alanine,valine, isoleucine, leucine, methionine, phenylalanine, tyrosine ortryptophan. In another alternative, residue 147 is cysteine or proline.In another alternative, residue 147 is aspartic acid or glutamic acid.

By site-specific mutagenesis of the crucial lysine (K) into an arginine(R), frataxin K147R, a frataxin mutant that is not ubiquitinated wasgenerated. Because frataxin K147R cannot be ubiquitinated, it isrelatively resistant to proteasome-mediated degradation.

Frataxin mutants that have a residue other than lysine at position 147,including frataxin K147R, are introduced into frataxin-defective cellsvia one of several procedures. The protein can be delivered directly orafter loading into liposomes, polymeric microcarriers, exosomes orbacterial carriers, either with or without having been fused to aprotein transduction domain. Frataxin mutants can also be delivered tocells by packaging a viral, hybrid synthetic-viral, or non-viral systemwith mutant FXN cDNA and then administering to a subject. A subjecthaving a frataxin deficiency can be effectively treated by receiving atherapeutically effective amount of a pharmaceutical composition offrataxin K147R, which optionally includes pharmaceutically acceptableexcipients.

In some aspects, the present disclosure provides isolated polypeptidehaving at least 75%, 80%, 85%, 90%, 95%, 98%, or 99% sequence identityto SEQ ID NO: 1 and comprising a residue other than lysine at positioncorresponding to position 147 of SEQ ID NO: 1. In one aspect, thepresent disclosure provides isolated polypeptide having at least 75%,80%, 85%, 90%, 95%, 98%, or 99% sequence identity to SEQ ID NO: 1 andcomprising an R residue at a position corresponding to position 147 ofSEQ ID NO: 1.

In some aspects, the present disclosure provides for isolated nucleicacid molecule comprising a nucleic acid sequence which encodes apolypeptide having at least 75%, 80%, 85%, 90%, 95%, 98%, or 99%sequence identity to SEQ ID NO: 1.

In some aspects, the present disclosure provides for isolated nucleicacid molecules, wherein the nucleic acid molecule comprises a nucleotidesequence having at least 75%, 80%, 85%, 90%, 95%, 98%, or 99% sequenceidentity to SEQ ID NO: 2.

A more stable frataxin as a therapeutic tool. The FXN mutation of thesingle residue K147 into a residue other than lysine confers stabilityto the frataxin precursor and allows the generation of larger amounts ofmature frataxin. In one embodiment, arginine replaces K 147. Theincreased stability of frataxin K147R compared to wild type frataxin canbe a clear advantage for both gene-based and protein-based replacementtherapeutic approaches to the treatment of Friedreich's Ataxia.Specifically, the frataxin K147R mutant is useful in the following areasof therapeutic intervention:

a) Protein delivery. Frataxin K147R can be delivered tofrataxin-defective cells after loading into conventional liposomes,either as unilamellar vesicles (ULV) or multilamellar vesicles (MLV), asdescribed in (Balasubramanian et al., 2010; Torchilin, 2005; Walde andIchikawa, 2001) and references therein. To increase liposome stability,liposomes can be coated with polyethylene glycol (PEG) or encapsulatedinto polymeric matrices, such as chitosan (Werle and Takeuchi, 2009),alginate (Dai et al., 2006), or others. More stable encapsulatedliposomes (capsosomes) can also be used, as described in (Stadler etal., 2009), or other liposomes (trigger liposomes) that release theircontent after an external trigger found in specific tissues or metabolicconditions can be used as well, as described in (Chen et al., 2004).

Alternatively, frataxin K147R can be delivered after entrapping intopolymeric microcarriers, such as poly(lactic-co-glycolic) acidmicroparticles, as described in (Kim et al., 2009), long-lastingpoly(e-caprolactone) (Coccoli et al., 2008), polyanhydrides such aspoly(1,3-bis-(p-carboxyphenoxypropane)-co-sebacic anhydride) (P(CPP-SA))microspheres (Sun et al., 2009), or core-shell microcapsules (Haidar etal., 2008). Frataxin K147R delivery can be achieved using more efficientsystems such as polymeric nanoparticles (Singh and Lillard, 2009)(Hasadsri et al., 2009), polymeric micelles (Miller et al., 2009) orpolymersomes (Onaca et al., 2009) (Christian et al., 2009), usingpolystyrene (Zauner et al., 2001), poly(lactic-co-glycolic) acid(Garnacho et al., 2008), PEG (Christian et al., 2009) (Dziubla et al.,2005) or other polymers.

Frataxin K147R can also be introduced into frataxin-defective cells byusing bacteria such as Listeria monocytogenes as a delivery vehicle(Dietrich et al., 1998; Ikonomidis et al., 1997), or after entrapmentinto exosomes, which are naturally occurring nanovesicles released bycells (Simons and Raposo, 2009). Furthermore, frataxin K147R can bedelivered by fusing it to antibodies or peptides, adding glycosylationsites, removing sites involved in activation, or PEGylating the proteinby covalently attaching polyethylene glycol to the protein (Goodson andKatre, 1990). Finally, frataxin K147R can be directly administered viatraditional methods of protein delivery such as microinjection andelectroporation.

Delivery of frataxin K147R into frataxin-defective cells can be greatlyenhanced by the use of protein transduction domains (PTD), includingTAT, Antp, VP22 and others. The 11 peptide of the HIV-1 TAT protein isthe most extensively investigated among PTDs (Rapoport andLorberboum-Galski, 2009). TAT, or other PTDs, can therefore be used tomodify liposomes, microcarriers, nanoparticles, micelles or exosomescontaining frataxin K147R in order to facilitate entry into cells.

TAT or other PTDs can be directly fused in frame with frataxin K147R fora direct protein delivery approach to frataxin-defective cells, asdescribed for other mitochondria-targeted proteins (Rector et al., 2008)(Rapoport et al., 2008).

In an example that closely resembles the intended delivery of frataxininto the mitochondria of FRDA cells, the mitochondrial protein lipoamidedehydrogenase (LAD), was in fact fused with TAT in a tentativetherapeutic strategy to cure LAD deficiency (Rapoport et al., 2008). LADdeficiency (Maple syrup urine disease) is a rare autosomal recessiveneurological disorder caused by mutations in the lipoamide dehydrogenasegene, and results in defective activity of LAD, a mitochondrial enzymeinvolved in amino acid and carbohydrate metabolism. Similarly tofrataxin, the LAD precursor is imported into the mitochondria andsubsequently proteolytically processed into a mature functional form.

Frataxin K147R can therefore be cloned downstream of TAT in a pTATplasmid. The resulting construct can be used to transform E. colicompetent cells, and then the TAT-frataxin K147R fusion proteinrecovered from the bacteria supernatant can be purified by proteinliquid chromatography or by other methods (Rapoport et al., 2008). Totest the activity of the purified product, the TAT-frataxin K147R fusionprotein can be directly delivered to FRDA fibroblasts or lymphoblasts inculture, and subsequently the amount of intracellular andintramitochondrial frataxin can be quantitated by SDS-PAGE and westernblot analysis. Assays commonly used to functionally test frataxin incells, such as aconitase enzymatic activity, can be used to confirm thefunctional recovery of FRDA cells after the exposure to the TAT-frataxinK147R fusion protein. The efficacy of the TAT-frataxin K147R fusionprotein can subsequently be tested in the available mouse model of FRDA,either by direct systemic infusion or by systemic infusion afterencapsulation into any of the previously described micro ornanocarriers. Treated mice can then be scored biochemically(quantitation of frataxin levels in multiple tissues) and phenotypically(delay in disease progression, amelioration of sensomotory performance,etc.) for efficacy evaluation.

In all of the above mentioned examples of protein delivery, thepossibility of loading the liposomes, microcarriers or exosomes with amore stable form of frataxin, i.e., the frataxin K147R mutant, or thepossibility of fusing any PTD with a more stable form of frataxin, i.e.,the frataxin K147R mutant, might result in a longer bioavailability ofthe administered frataxin, compared to similar approaches usingwild-type frataxin, with possible reduction in the administrationregimen, dosage, etc. that can reduce costs as well as discomfort andside effects for the patients.

In certain aspects, the present disclosure provides for methods ofdelivering the isolated polypeptide of any of the present disclosureinto a cell by a carrier selected from the group consisting of aliposome, a polymeric microcarrier, an exosome, a bacterial carrier, anda functional equivalent thereof. In further aspects, the isolatedpolypeptide has been fused in frame with a protein transduction domain.In still further aspects, the isolated polypeptide is delivered into thecell of a subject having Friedreich's Ataxia.

In some aspects, the present disclosure provides for methods ofdelivering the isolated polypeptide of the present disclosure into acell by a carrier system selected from the group consisting of a viralsystem, a hybrid synthetic-viral system, a non-viral system, and afunctional equivalent thereof.

b) Gene therapy. Gene therapy for neurodegenerative diseases isattempted using viral or non-viral systems, as summarized in (Nanou andAzzouz, 2009) and references cited therein. Viral systems includeadenoviruses, adeno-associated viruses, retroviruses, lentiviruses,herpes viruses, vaccinia viruses, poxviruses and others (Cardone, 2007)(Lim et al., 2010). Non-viral systems can make use of naked DNA orliposomes as carriers. Hybrid synthetic-viral systems can also be used(Nanou and Azzouz, 2009), as well as bacterial systems such asEscherichia coli or Shigella flexneri (Sizemore et al., 1995; Courvalinet al., 1995). Gene therapy approaches for FRDA, using a cDNA coding forthe frataxin K147R mutant, can therefore be attempted using any of thesesystems.

Lentivirus-derived vectors in particular have been shown to alloweffective gene expression in Spinal Muscolar Atrophy (SMA), anotherinherited monogenic disease characterized by peripheral neuron loss. SMAis due to mutations or deletion of the survival motor neuron (SMN) geneleading to depletion of SMN, a nuclear and cytoplasmic protein requiredfor motorneuron survival. In an animal model for SMA, an equineinfectious anemia virus (EIAV)-based lentivector, pseudotyped withrabies-G virus, has been shown to be effective in retrograde axonaltransport and has been used to transduce spinal cord neurons followingviral injections into muscles (Azzouz et al., 2004).

The frataxin K147R cDNA can therefore be cloned into aself-inactivating, rabies-G pseudotyped EIAV-based transfer vector(Azzouz et al., 2002). The EIAV-frataxin K147R lentivector can be firsttested for its ability to express and reconstitute frataxin infrataxin-defective cells, by in vitro exposure to FRDA fibroblasts andsubsequent quantitation by SDS-PAGE and western blot analysis. Assayscommonly used to functionally test frataxin in cells, such as aconitaseenzymatic activity, can be used to confirm the functional recovery ofFRDA cells after lentivector exposure. The EIAV-frataxin K147Rlentivector will then be injected at multiple sites into peripheralmuscles of FRDA mice. Treated mice will then be scored biochemically(quantitation of frataxin levels in multiple tissues) and phenotypically(delay in disease progression, amelioration of sensomotory performance,etc.) for efficacy evaluation.

In all of the above mentioned examples of gene therapy, the possibilityto package viral, non-viral or hybrid systems with a gene coding for amore stable form of frataxin, i.e., the frataxin K147R mutant, mightresult in a longer bioavailability of the expressed frataxin compared tosimilar approaches using wild type frataxin, with possible reduction inthe administration regimen, dosage, etc. that can reduce costs as wellas discomfort and side effects for the patients.

In some aspects, the present disclosure provides for pharmaceuticalcompositions comprising a therapeutically effective amount of theisolated polypeptide of the present disclosure, optionally together withone or more pharmaceutically acceptable excipients, diluents,preservatives, solubilizers, emulsifiers, adjuvants, or carriers.

Furthermore, a method of treating frataxin deficiency can includeadministering to a subject a therapeutically effective amount of apharmaceutical composition of the frataxin K147R mutant. Thispharmaceutical composition can further comprise one or morepharmaceutically acceptable excipients to provide a pharmaceuticalcomposition. Exemplary excipients include, without limitation,carbohydrates, inorganic salts, antimicrobial agents, antioxidants,surfactants, buffers, acids, bases, and combinations thereof. Excipientssuitable for injectable compositions include water, alcohols, polyols,glycerine, vegetable oils, phospholipids, and surfactants. Acarbohydrate such as a sugar, a derivatized sugar such as an alditol,aldonic acid, an esterified sugar, and/or a sugar polymer can be presentas an excipient. Specific carbohydrate excipients include, for example:monosaccharides, such as fructose, maltose, galactose, glucose,D-mannose, sorbose, and the like; disaccharides, such as lactose,sucrose, trehalose, cellobiose, and the like; polysaccharides, such asraffinose, melezitose, maltodextrins, dextrans, starches, and the like;and alditols, such as mannitol, xylitol, maltitol, lactitol, xylitol,sorbitol (glucitol), pyranosyl sorbitol, myoinositol, and the like. Theexcipient can also include an inorganic salt or buffer such as citricacid, sodium chloride, potassium chloride, sodium sulfate, potassiumnitrate, sodium phosphate monobasic, sodium phosphate dibasic, andcombinations thereof.

A composition of the invention can also include an antimicrobial agentfor preventing or deterring microbial growth. Nonlimiting examples ofantimicrobial agents suitable for the present invention includebenzalkonium chloride, benzethonium chloride, benzyl alcohol,cetylpyridinium chloride, chlorobutanol, phenol, phenylethyl alcohol,phenylmercuric nitrate, thimersol, and combinations thereof.

An antioxidant can be present in the composition as well. Antioxidantsare used to prevent oxidation, thereby preventing the deterioration ofthe mutant frataxin K147R or other components of the preparation.Suitable antioxidants for use in the present invention include, forexample, ascorbyl palmitate, butylated hydroxyanisole, butylatedhydroxytoluene, hypophosphorous acid, monothioglycerol, propyl gallate,sodium bisulfite, sodium formaldehyde sulfoxylate, sodium metabisulfite,and combinations thereof.

A surfactant can be present as an excipient. Exemplary surfactantsinclude: polysorbates, such as “Tween 20” and “Tween 80,” and pluronicssuch as F68 and F88 (BASF, Mount Olive, N.J.); sorbitan esters; lipids,such as phospholipids such as lecithin and other phosphatidylcholines,phosphatidylethanolamines (although preferably not in liposomal form),fatty acids and fatty esters; steroids, such as cholesterol; chelatingagents, such as EDTA; and zinc and other such suitable cations.

Acids or bases can be present as an excipient in the composition.Nonlimiting examples of acids that can be used include those acidsselected from the group consisting of hydrochloric acid, acetic acid,phosphoric acid, citric acid, malic acid, lactic acid, formic acid,trichloroacetic acid, nitric acid, perchloric acid, phosphoric acid,sulfuric acid, fumaric acid, and combinations thereof. Examples ofsuitable bases include, without limitation, bases selected from thegroup consisting of sodium hydroxide, sodium acetate, ammoniumhydroxide, potassium hydroxide, ammonium acetate, potassium acetate,sodium phosphate, potassium phosphate, sodium citrate, sodium formate,sodium sulfate, potassium sulfate, potassium fumerate, and combinationsthereof.

The amount of the mutant frataxin K147R (e.g., when contained in a drugdelivery system) in the composition will vary depending on a number offactors, but will optimally be a therapeutically effective dose when thecomposition is in a unit dosage form or container (e.g., a vial). Atherapeutically effective dose can be determined experimentally byrepeated administration of increasing amounts of the composition inorder to determine which amount produces a clinically desired endpoint.

The amount of any individual excipient in the composition will varydepending on the nature and function of the excipient and particularneeds of the composition. Typically, the optimal amount of anyindividual excipient is determined through routine experimentation,i.e., by preparing compositions containing varying amounts of theexcipient (ranging from low to high), examining the stability and otherparameters, and then determining the range at which optimal performanceis attained with no significant adverse effects.

The compositions encompass all types of formulations and in particularthose that are suited for injection, e.g., powders or lyophilates thatcan be reconstituted with a solvent prior to use, as well as ready forinjection solutions or suspensions, dry insoluble compositions forcombination with a vehicle prior to use, and emulsions and liquidconcentrates for dilution prior to administration. Examples of suitablediluents for reconstituting solid compositions prior to injectioninclude bacteriostatic water for injection, dextrose 5% in water,phosphate buffered saline, Ringer's solution, saline, sterile water,deionized water, and combinations thereof. With respect to liquidpharmaceutical compositions, solutions and suspensions are envisioned.Additional preferred compositions include those for oral, ocular, orlocalized delivery.

The pharmaceutical preparations herein can also be housed in a syringe,an implantation device, or the like, depending upon the intended mode ofdelivery and use. Preferably, the mutant frataxin K147R compositionsdescribed herein are in unit dosage form, meaning an amount of aconjugate or composition of the invention appropriate for a single dose,in a premeasured or pre-packaged form.

Having now generally described various aspects and embodiments of theinvention, the same will be more readily understood through reference tothe following examples which are provided by way of illustration, andare not intended to be limiting, unless specified.

EXEMPLARY ASPECTS EXAMPLE 1 DNA Constructs

The pcDNA3-frataxin-HA construct was generated by subcloning the 3′HA-tagged frataxin from pBS-frataxin-HA into the pcDNA3 vector. Thelysine mutant constructs were generated using the Quick-Changesite-directed mutagenesis kit (Stratagene) with specific primers usingeither pcDNA5-frataxin or pcDNA3-frataxin-HA, as template. All theconstructs generated were verified by DNA sequencing.

EXAMPLE 2 Immunoblotting

Antibodies. The following antibodies were used for western blotanalysis: mAb anti-frataxin (MAB-10876, Immunological Science), mAbanti-HA (clone HA-7, Sigma), mAb anti-tubulin (Sigma), secondaryantibody HRP-conjugated goat anti-mouse (Pierce).

Immunoblotting. Cell extracts were prepared in modified RIPA buffer (10mM sodium phosphate pH7.2, 150 mM NaCl, 1% Na deoxycholate, 0.1% SDS, 1%Np40, 2 mM EDTA) or IP buffer (50 mM Tris-HCl, pH 7.5, 150 mM NaCl, 1%Nonidet P-40, 5 mM EDTA, 5 mM EGTA) supplemented with Complete proteaseinhibitor cocktail and 2 mM N-Ethylmaleimide (NEM). For immunoblotting,100 μg of protein extract were separated on 12% SDS-PAGE, blotted ontonitrocellulose membrane and detected with specific antibodies. Allimmunoblots were revealed by ECL (GE Healthcare). Densitometric analysiswas performed using ImageJ software.

EXAMPLE 3 Frataxin K147R Resistance to Proteasome-Mediated Degradation

The frataxin K147R mutant was stably expressed in Flp-In-293 cells totest whether the loss of the ubiquitin docking site granted the frataxinK147R mutant a relative resistance to proteasome-mediated degradation,thus increasing its stability. Flp-In-293 cells (Invitrogen) are humanembryonic kidney HEK293 variants allowing the stable and isogenicintegration and expression of a transfected gene. Flp-In-293 cells weremaintained in DMEM supplemented with 10% FBS and transfected with thecalcium/phosphate precipitation method. Briefly, cells were plated on 10cm dishes and transfected with 10 μg total DNA. pcDNA5-frataxin K147Rwas used for the generation of 293 Flp-In stable cell line. Flp-In-293cells stably expressing frataxin K147R were obtained from cultures inselection medium containing 100 μg/ml hygromycin B (Invitrogen). Afterexposure to cycloheximide to block new protein synthesis, the stabilityof the frataxin K147R precursor was monitored over time and compared tothe stability of a wild type frataxin¹⁻²¹⁰ precursor stably expressed inFlp-In-293 cells and similarly treated. FIGS. 3A-B shows that thefrataxin K147R precursor is significantly more stable (˜45% of the inputafter 24 hrs) than the frataxin¹⁻²¹⁰ precursor (˜15% of the input after24 hrs).

EXAMPLE 4 Frataxin K147R Stability

In a different set of experiments, the HA-tagged frataxin K147R mutantor the HA-tagged wt frataxin¹⁻²¹⁰ was transiently expressed in HeLacells using pcDNA3-frataxin-HA K147R. Hela cells were maintained in DMEMsupplemented with 10% FBS and transfected using Lipofectamine 2000reagents (Invitrogen), according to manufacturer's instructions. Thisapproach forces the ectopic expression of frataxin and allows thedetection of all processing products, including the mature frataxin. Thepersistence of frataxin K147R was followed over a 5 day period upontransfection and compared to wild type frataxin. FIG. 4 shows thatfrataxin K147R is correctly processed and that its expression allows theaccumulation of higher levels of frataxin precursor, intermediate andmature frataxin. Importantly, a significant amount of mature frataxinK147R can still be observed 3 days after transfection, a time pointwhere wild type mature frataxin is no longer detectable.

The description of the aspects of the invention has been presented forthe purpose of illustration; it is not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Persons skilled inthe relevant art can appreciate that many modifications and variationsare possible in light of the above teachings. It should be noted thatthe language used in the specification has been principally selected forreadability and instructional purposes, and it may not have beenselected to delineate or circumscribe the inventive subject matter.Accordingly, the disclosure of the aspects of the invention is intendedto be illustrative, but not limiting, of the scope of the invention.

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What is claimed:
 1. A polypeptide having at least 90% sequence identityto SEQ ID NO:1 and comprising an R residue at a position correspondingto position 147 of SEQ ID NO:1.
 2. The polypeptide of claim 1, whereinthe polypeptide has at least 95% sequence identity to the amino acidsequence of SEQ ID NO:1.
 3. The polypeptide of claim 1, wherein thepolypeptide has at least 99% sequence identity to the amino acidsequence of SEQ ID NO:1.
 4. An isolated or recombinant polynucleotidecomprising or consisting of a nucleic acid sequence which encodes apolypeptide having the amino acid sequence of
 1. 5. The polynucleotideof claim 4, wherein the nucleic acid molecule comprises a nucleotidesequence having at least 90% sequence identity to the full lengthsequence of SEQ ID NO:2.
 6. An isolated or recombinant polynucleotidecomprising or consisting of a nucleotide sequence having at least 90%sequence identity to the full length sequence of SEQ ID NO:2.
 7. Avector comprising the polynucleotide of claim
 4. 8. A host cellcomprising the polynucleotide of claim
 4. 9. A pharmaceuticalcomposition comprising a therapeutically effective amount of theisolated polypeptide of claim 1, optionally together with one or morepharmaceutically acceptable excipients, diluents, preservatives,solubilizers, emulsifiers, adjuvants, or carriers.
 10. A method oftreating Friedreich's Ataxia, comprising administering to a subject thepharmaceutical composition of claim
 9. 11. A method of delivering theisolated polypeptide of claim 1, into a cell by a carrier selected fromthe group consisting of a liposome, a polymeric microcarrier, anexosome, a bacterial carrier, and a functional equivalent thereof. 12.The method of claim 9, wherein the isolated polypeptide has been fusedin frame with a protein transduction domain.
 13. The method of claim 9,wherein the isolated polypeptide is delivered into the cell of a subjecthaving Friedreich's Ataxia.
 14. A method of delivering the isolatedpolypeptide of claim 1 into a cell by a carrier system selected from thegroup consisting of a viral system, a hybrid synthetic-viral system, anon-viral system, and a functional equivalent thereof
 15. The method ofclaim 14, wherein the isolated polypeptide is delivered into the cell ofa subject having Friedreich's Ataxia.
 16. A method of preventingproteasome-mediated degradation of frataxin in a cell comprisingexpressing the polypeptide of claim 1 in the cell.
 17. A method ofpreventing ubiquitination of frataxin in a cell comprising expressingthe polypeptide of claim 1 in the cell.
 18. A method of preventingproteasome-mediated degradation of frataxin in a cell comprisingintroducing the polypeptide of claim 1 in the cell.
 19. A method ofpreventing ubiquitination of frataxin in a cell comprising introducingthe polypeptide of claim 1 in the cell.